The present invention is directed to electrochemically etching and, more particularly, is directed to electrochemically etching a workpiece from the center outwardly in a spiral pattern.
Electrochemical etching has many industrial applications wherein a conductive metal is etched from the surface of a workpiece. The present inventors have proposed a new apparatus and method for electrochemical etching which has wide industrial application. The present invention, however, has particular application to the electrochemical etching of semiconductor wafers and so the present invention will only be discussed in reference to semiconductor wafers, although it should be understood that the present invention has wider industrial application.
Electroetching involves metal removal from a workpiece which is made an anode in an electrolytic cell. The cell contains a counter electrode (cathode) at an appropriate position. In the microelectronics industry, electroetching is used for through-mask patterning and for removal of continuous thin film of conducting metals, such as seed layers from the surface of a semiconductor wafer. Different types of electroetching apparatus are described in the literature that use a variety of electrolyte flow systems ranging from non-agitated to impinging jets. For electroetching of large wafers, such as 200 mm, the electroetching systems pose problems of high power requirement and tremendous edge effects that lead to the loss of electrical connection to the metal film.
In order to alleviate the above problems, Datta et al. U.S. Pat. No. 5,284,554, and U.S. Pat. No. 5,486,282, the disclosures of which are incorporated by reference herein, proposed to treat only a small portion of the wafer at a given time by using a multinozzle cathode assembly of small width which delivers the electrolyte to a part of the wafer that faces the cathode assembly. During electroetching, the multinozzle assembly is slowly scanned from one end of the wafer to the other end. The nozzle movement is adjusted to match the etching rate of film so that the wafer etching is completed in one pass. Additional Patents reflecting further improvements to the above work include Dinan et al. U.S. Pat. No. 5,536,388 and Datta et al. U.S. Pat. No. 5,567,304, the disclosures of which are incorporated by reference herein.
Notwithstanding the prior art solutions to the problem, there remains a need to improve electrochemical etching. The present inventors have proposed to change the way in which the electrolyte contacts the wafer surface. Rather than using a linear trough for the electrolyte and contacting the wafer across a chord with dependence on an ever-decreasing number of contact points, the present inventors have proposed an apparatus and method with an annular contact path so that this dependence on an ever-decreasing number of contact points is eliminated.
Thus, a purpose of the present invention is to have an apparatus and method for electrochemical etching which does not use a linear trough for the electrolyte.
It is another purpose of the present invention to have an apparatus and method for electrochemical etching which does not depend on an ever-decreasing number of contact points.
These and other purposes of the present invention will become more apparent after referring to the following description considered in conjunction with the accompanying drawings.